Pipette assembly

ABSTRACT

A pipette assembly for accurate aspiration and discharge of fixed amounts from a pipette tip is disclosed. A spring-biased cylinder is mounted for rotation about its longitudinal axis for selecting the desired volume of liquid to be discharged. A variable volume control chamber is defined between the ID of the cylinder and the OD of a stationary piston rod. Reciprocation of the cylinder varies the volume of the control chamber.

United States Patent 1191 Sokol et al.

1451 Sept. 25, 1973 PIPETTE ASSEMBLY [75] Inventors: Michael Sokol,Abington; Frederick M. Kent, Warrington, both of Pa.

[73] Assignee: Bio/Data Corporation, Hatboro, Pa.

[22] Filed: Oct. 20, 1972 21 Appl. No.: 299,552

[52] US. Cl. 73/425.6 [51] Int. Cl B011 3/02 [58] Field of Search73/425.4 R, 425.4 P,

73/425.6; 222/43, 309, 386; 128/218 A, 218 R, 218 C, 218 F, 234, 236;23/259, 292

[56] References Cited UNITED STATES PATENTS 3,244,099 4/1966 Tietje73/425.6

3,494,201 2/1970 Roach 73/425.6

Primary Examiner-S. Clement Swisher Att0rneyArthur l-l. Seidel et a].

I [57] ABSTRACT A pipette assembly for accurate aspiration and discharge of fixed amounts from a pipette tip is disclosed. A spring-biasedcylinder is mounted for rotation about its longitudinal axis forselecting the desired volume of liquid to be discharged. A variablevolume control chamber is defined between the ID of the cylinder and theOD of a stationary piston rod. Reciprocation of the cylinder varies thevolume of the control chamber.

10 Claims, 6 Drawing Figures PIPETTE ASSEMBLY This invention is directedto a manually operable pipette assembly which is more accurate than theprior art, reduces mechanical handling during usage, and increases theefficiency in dispensing at a constant rate of discharge.

A typical example of the prior art is shown in U. S. Pat. No. 3,290,946dated Dec. 13, 1966. When the plunger in said patent is pushed in, it isnecessary to keep ones finger over the hole in the plunger. Thereafter,the plunger is permitted to reciprocate away from the pipette tip toaspirate liquid into the pipette while at all times maintaining a fingerover the hole of the plunger. Thereafter, dispensing is attained byremoving ones finger from the hole in the plunger. Thus, the prior artis a three-step process while relying on finger manipulation andjudgment for accuracy as to the amount of liquid being dispensed.

In the present invention, thenumber of steps is reduced when using thepipette assembly while at the same time the operator has the ability todispense a predetermined small amount of liquid with accuracy in excessof 99 percent. Further, the pipette assembly of the present invention isless expensive and easier to assemble than some prior art devices. Whilethe pipette assembly has a variety of uses, it is particularly adaptedfor use in connection with a blood coagulation analyzer such as thatdisclosed in U. S. Pat. No. 3,658,480 dated Apr. 25, 1972 wherein theamount of liquid beingdispensed by the pipette assembly must beaccurately controlled. I

It is an object of the present invention to provide a novel pipetteassembly. I

It is another object of the present invention to provide a pipetteassembly for accurately dispensing small amounts of liquids.

minum, but may be made of other materials and may have othercross-sections. The housing 12 has first and second ends.

The first end of the housing 12 is provided with threads on its innerperiphery engaged with threads on the outer periphery of a reduceddiameter portion 16 of a pipette support designated generally as 14. Thepipette support 14 is in the form of a nose with a constantly reducingcross-sectional area from the diameter of the housing 12 down to thediameter of an axial barrel. The pipette support 14 is provided with anaxial bore 18 therethrough and terminates at its free end in a'reduceddiameter portion 20. The reduced-diameter portion 20 is adapted toremovably receive an expendable hollow pipette tip 22. The pipette tip22 may be a disposable pipette of high density, rigid polymeric plasticmaterials such as polypropylene.

The second end of the housing 12 is closed by means of an adapter 24.The adapter 24 has an end face 25 and a shoulder 26 for contact withanlend of the housing 12. Threads on, the ID of said second end of thehousing 12 are engaged with threads on the OD of said adapter 24. Itwill be noted that the adapter 24 extends into the second end of thehousing 12 and terminates in a reduced diameter portion 28 having anaxial bore 30. v

A hollow rod 32 has one end threadedly coupled to I the pipette support14. A bore 34 in the rod 32 commu- It is another object of the presentinvention to pro- I vide a pipette assembly which is easy to assembleand requires fewer steps during usage.

It is another object of the present invention to provide a pipetteassembly wherein the user may'selectively choose one of several fixedamounts of liquids to be dispensed.

Other objects will appear hereinafter.

' For the purpose of illustrating the invention, there is shown in thedrawings a form which is presently preferred; it being understood,however, that this invention is not limited to the precise arrangementsand instrumentalities shown.

FIG. 1 is a perspective view of a pipette assembly in accordance withthe present invention.

FIG. 2 is a sectional view taken along the line 22 in FIG. 1.

FIG. 3 is a sectional view similar to FIG. 2, but illustrating thecomponents in their relative position when the spring is compressed.

FIG. 4 is a perspective view of the adapter shown in FIG. 1, but'on alarger scale.

FIG. 5 is a perspective view of the end of the adapter in FIG. 4, but ona larger scale.

FIG. 6 is a perspective view of the end of the adapter in FIG. 4, but ona larger scale.

nicates directly with the bore 18 and the interior of the pipette-tip22.

A head 36 has a reduced diameter portion telescoped into and fixedlysecured to the other end of hollow rod 32 in any manner such as by aforce fit. A seal 38 is supported by the head 36 and clamped against theend face of rod 32. Seal 38 will perform the function of a piston. Thus,rod 32 may be referred to as a piston rod.

A cylinder 40 is disposed within the housing 12 and surrounds a portionof the rod 32. Cylinder 40 is spaced from the outer periphery of rod 32to define a chamber .therebetween designated 46. Seal 38 engages the IDof cylinder 40 and constitutes a sealing means for one end of thechamber 46. A cap 42 is connected to the cylinder 40 in any convenientmanner such as by threads. Cap 42 cooperates with a seal 44 which isclamped against an end face of the cylinder 40. Seal 44 seals theReferring to the drawing in detail, wherein like nuignated generally as10. The assembly 10 includes a housing 12. Housing 12 is preferably acylinder of aluother end of chamber 46. Chamber 46 communicates with thebore 34 by means of one or more passages 48 in the rod 32. The passages48 are in the nature of bleed holes.

The cylinder 40 is provided with a limit stop 50 which may take the formof a radially outwardly directed pin. The reduced diameter portion 28 onthe adapter 24 is provided with circumferentially spaced recesses 52, 54and 56, each adapted to selectively receive the pin 50 and thereby limitthe extent of movement of the cylinder 40 in a direction away from thepipette support 14. The depth of the recesses 52, 54 and 56 is eachdiffer- In a typical embodiment, the depth of the recess 56 is 0.742inch and is chosen so as to result in a discharge of 0.2 ml from thepipette tIp 22. Also, the depth of recess 54 was 0.355 inch to result ina discharge of 0.1 ml from the pipette tip 22. Also, the depth of recess52 was 0.158 inch so as to discharge 0.05 ml from the pipette tip 22.The depth of the recesses 52-56 and other related dimensions on othercomponents may be varied as desired to effect any particular volume ofdischarge from the pipette tip 22.

In order that the desired volumetric discharge may be selectivelyattained, the assembly includes a selector 58 having a reduced diameterportion telescoped into and fixedly secured to the cylinder 40 in anydesired manner such as a force fit. The selector 58 is provided with aplurality of pointers 60 circumferentially disposed about the selector58 and preferably each of a different color. Each pointer 60 may beselectively aligned with an indicator point 61 on the end face 25 of theadapter 24. Adapter 24 is provided with a stepped bearing 62 tofacilitate rotational support of the casing 40 about its longitudinalaxis.

, The rod 32 is stationary. The cylinder 40. may rotate about its axisand is also adapted for movement in an axial direction. A spring 64surrounds the hollow rod 32. One end of spring 64 engages a face 66 onthe pipette support 14. The other end of spring 64 engages the cap 42and biases the cylinder 40 in a direction away from the pipette support14. In FIG. 3, the spring 64 has been compressed to its maximum extent,chamber 46 has its maximum volume, and the selector 58 has contacted thebearing 62. In FIG. 2, the spring 64 has expanded to the extentpermitted by entry of the limit stop 50 into the recess 54.

The pipette assembly may be used as follows: The volume of liquid to bedischarged is first selected by pushing on selector 58 until limit stop50 is outside the recesses 52, 54 and 56. Then the selector 58 isrotated. The pointer 60 may be supplemented with numerical indicia. Whenthe pointer 60 is aligned with anindicator 61 on the end face 25, limitstop 50 will be aligned with one of the recesses 52, 54, and 56. Thenpressure on selector 58 is released so that the cylinder 40 reciprocatesin an axial direction, under the bias of spring 64, until the limit stop50 bottoms out in the selected recess. As shown in FIGS. 4f-6, each ofthe recesses 52, 54 and 56 is generally V-shaped at least at the endface of portion 28 to make it easy for the limit stop 50 to enter itsrecess and take into consideration that the components are slightlymisaligned.

Thereafter, the assembly 10 is held in a position so that the pipettetip 22 is immersed in the liquid. Then, the selector 58 is manuallypushed until it bottoms out as shown in FIG. 3. As the selector 58 andcylinder 40 move in an axial direction, the spring 64 is compressed andthe volume of chamber 46 increases by the selected amount. This createsa suction effect whereby the selected or desired amount of the liquid isaspirated into the pipette 22. Thereafter, the assembly 10 is moved to alocation wherein the pipette tip 22 is juxtaposed to the desiredreceptacle such as a test tube. The finger pressure applied to theselector 58 may then be released permitting the spring 64 to expand andeffect discharge from the pipette tip 22 into the receptacle.

As the spring 64 expands, dischrage from pipette tip 22 is at the rateof expansion of the spring 64. Dis charge may be at a constant rate byusing spring 64 in the form of a constant force spring. Expansion of thespring 64 decreases the volume of chamber 46 and continues until thelimit stop 50 bottoms out in the selected recess 52, 54 or 56 on thereduced diameter portion 28 of the adapter 24. Since discharge of theliquid from the pipette tip 22 coincides with expansion of the spring64, any components of the liquid are intimately mixed while beingdischarged and are further mixed with any liquid in the receptacle.

Since discharge is at the rate of expansion of spring 64, discharge isat a rate substantially greater than the rate of discharge under theeffect of gravity. Thus, the liquid being discharged is pushed out ofthe end of pipette tip 22 by a column of pressurized air in rod 32 andchamber 46. Hence, discharge need not be in a downward direction. Theassembly 10 has been found to have a volumetric accuracy of 99.75percent. Such accuracy is difficult to attain with prior art deviceswhen dealing with small volumes as described above.

The entire assembly 10, if desired, may be made from materials so thatit may be sterilized. In the event of an overfill of liquid,contamination may be prevented by making the cylinder 40, hollow rod 32,and head 36 from stainless steel. The remaining elements are preferablymade from non-corrosive materials such as aluminum, brass and the like.

While selection of the amount to be dispensed is preferably attained byrotating the cylinder relative to adapter 24, it is within the scope ofthe invention te attain such selection by rotating adapter 24 relativeto cylinder 40 which would be limited to axial movement.

The present invention may be embodied in other specific forms withoutdeparting from the spirit or essential attributes thereof and,accordingly, reference should be made to the appended claims, ratherthan to the foregoing specification as indicating the scope of theinvention.

We claim:

1. A pipette assembly comprising a housing having first and second ends,a pipette tip support coupledto said first end of said housing, saidsupport having a bore therethrough, a stationary hollow rod in saidhousing and communicating with said bore, a cylinder in said housingsurrounding said rod and spaced therefrom to define a chamber ofvariable volume, the volume of said chamber increasing when saidcylinder moves toward said pipette tip support, sealing means betweensaid rod and cylinder for sealing the ends of said chamber, spring meansbiasing said cylinder away from said pipette tip support to effect adecrease in the volume of said chamber, said rod having a passagecommunicating with said chamber, and limit stop means for limiting theextent of movement of said cylinder in a direction away from saidpipette tip support due to the bias of said spring means.

2. A pipette assembly in accordance with claim 1 .wherein said limitstop means is selectively operable to limit the extent of movement ofthe cylinder in a direction away from the pipette support topredetermined distances.

3. A pipette assembly in accordance with claim 2 wherein said limit stopmeans includes an adapter supported by said housing, said adapter havinga plurality of recesses of different depths, each adapted to receive thelimit stop member on said cylinder.

4. A pipette assembly in accordance with claim 1 wherein said cylinderis rotatably supported by the housing for rotation about the axis of thecylinder, and means connected to the cylinder for selectively rotatingthe cylinder about its axis relative to the housing.

5. A pipette assembly in accordance with claim 1 wherein said springmeans controls discharge at a rate defined by the rate of expansion ofthe spring means and greater than the rate of discharge under the effectof gravity.

6. A pipette assembly in accordance with claim 1 wherein said limit stopmeans includes an adapter supported by said housing, said adapter havinga plurality of circumferentially spaced recesses on an end thereof, saidadapter surrounding said cylinder, said cylinder having a limit stop pinadapted to enter each of said recesses, and means for selectivelyrotating one of said adapter and cylinder about the longitudinal axis ofthe cylinder.

7. A pipette assembly in accordance with claim 1 wherein said chambersurrounds said rod, a head closing said rod at the end of the rod remotefrom said pipette tip support, said sealing means for sealing the endsof said chamber including a piston connected to said hollow rod and aseal supported by said cylinder for movement therewith.

8. A pipette assembly comprising a support housing, a pipette tipsupport coupled to said housing, said sup port having a boretherethrough', a hollow rod in said housing and communicating with saidbore, a cylinder in said housing surrounding said rod and spacedtherefrom to define a chamber of variable volume, sealing means betweensaid rod and cylinder for sealing the ends of said chamber, meansdefining a passage communicating said chamber with the interior of saidrod, spring means biasing said cylinder away from said pipette tipsupport whereby discharge from said pipette tip is at the rate ofexpansion of the spring means, and means for selectively limiting theextent of movement of said cylinder to a plurality of predetermineddistances in a direction along the longitudinal axis of said cylinderdue to the bias of said spring means.

9. A pipette assembly in accordance with claim 8 wherein saidlast-mentioned means includes an adapter supported by said housing andhaving a plurality of circumferentially spaced recesses of differentdepths, and means for rotating said cylinder about its longitudinalaxis, a limit stop member secured to said cylinder and adapted to bereceived in said recesses.

10. A pipette assembly in accordance with claim 8 including a pipettetip removably mounted on said pipette tip support, said sealing meansincluding a piston connected to said rod and a seal supported by saidcylinder for movement with the cylinder, said spring means including acoil spring surrounding said rod.

1. A pipette assembly comprising a housing having first and second ends,a pipette tip support coupled to said first end of said housing, saidsupport having a bore therethrough, a stationary hollow rod in saidhousing and communicating with said bore, a cylinder in said housingsurrounding said rod and spaced therefrom to define a chamber ofvariable volume, the volume of said chamber increasing when saidcylinder moves toward said pipette tip support, sealing means betweensaid rod and cylinder for sealing the ends of said chamber, spring meansbiasing said cylinder away from said pipette tip support to effect adecrease in the volume of said chamber, said rod having a passagecommunicating with said chamber, and limit stop means for limiting theextent of movement of said cylinder in a direction away from saidpipette tip support due to the bias of said spring means.
 2. A pipetteassembly in accordance with claim 1 wherein said limit stop means isselectively operable to limit the extent of movement of the cylinder ina direction away from the pipette support to predetermined distances. 3.A pipette assembly in accordance with claim 2 wherein said limit stopmeans includes an adapter supported by said housing, said adapter havinga plurality of recesses of different depths, each adapted to receive thelimit stop member on said cylinder.
 4. A pipette assembly in accordancewith claim 1 wherein said cylinder is rotatably supported by the housingfor rotation about the axis of the cylinder, and means connected to thecylinder for selectively rotating the cylinder about its axis relativeto the housing.
 5. A pipette assembly in accordance with claim 1 whereinsaid spring means controls discharge at a rate defined by the rate ofexpansion of the spring means and greater than the rate of dischargeunder the effect of gravity.
 6. A pipette assembly in accordance withclaim 1 wherein said limit stop means includes an adapter supported bysaid housing, said adapter having a plurality of circumferentiallyspaced recesses on an end thereof, said adapter surrounding saidcylinder, said cylinder having a limit stop pin adapted to enter each ofsaid recesses, and means for selectively rotating one of said adapterand cylinder about the longitudinal axis of the cylinder.
 7. A pipetteassembly in accordance with claim 1 wherein said chamber surrounds saidrod, a head closing said rod at the end of the rod remote from saidpipette tip support, said sealing means for sealing the ends of saidchamber including a piston connected to said hollow rod and a sealsupported by said cylinder for movement therewith.
 8. A pipette assemblycomprising a support housing, a pipette tip support coupled to saidhousing, said support having a bore therethrough, a hollow rod in saidhousing and communicating with said bore, a cylinder in said housingsurrounding said rod and spaced therefrom to define a chamber ofvariable volume, sealing means between said rod and cylinder for sealingthe ends of said chamber, means defining a passage communicating saidchamber with the interior of said rod, spring means biasing saidcylinder away from said pipette tip support whereby discharge from saidpipette tip is at the rate of expansion of the spring means, and meansfor selectiveLy limiting the extent of movement of said cylinder to aplurality of predetermined distances in a direction along thelongitudinal axis of said cylinder due to the bias of said spring means.9. A pipette assembly in accordance with claim 8 wherein saidlast-mentioned means includes an adapter supported by said housing andhaving a plurality of circumferentially spaced recesses of differentdepths, and means for rotating said cylinder about its longitudinalaxis, a limit stop member secured to said cylinder and adapted to bereceived in said recesses.
 10. A pipette assembly in accordance withclaim 8 including a pipette tip removably mounted on said pipette tipsupport, said sealing means including a piston connected to said rod anda seal supported by said cylinder for movement with the cylinder, saidspring means including a coil spring surrounding said rod.